Afterglow is one of many photo editors at the App Store, but an intuitive control layout, tons of subtle effects, and several sharing options make it an interesting option for tweaking your images. The app's primary focus is posting your altered images to Instagram, but you have plenty of other options for sharing as well. Start by taking a picture with your camera or grabbing an image from your photo library.
Rather than dramatic changes, what Afterglow focuses on is perfecting your image with subtle filters and other tweaks. The interface has buttons across the bottom of the screen for basic color tweaks (saturation and contrast, for example), filters, afterglow effects, and basic tools for cropping, rotating, and flipping the image. You also get a revert button in the lower left if you want to discard all your changes.